A standard windshield wiper is comprised of a wiper arm normally pivoted at a lower end at the base of the windshield about an axis perpendicular to the longitudinal axis of the wiper arm and an upper end on which a blade assembly is pivoted about an axis perpendicular to a plane including the lower-end pivot axis and wiper-arm longitudinal axis. The assembly itself comprises a main yoke pivoted on the upper end of the wiper arm and normally extending generally parallel to the wiper arm. Upper and lower secondary yokes are pivoted to upper and lower ends of the main yoke and tertiary yokes are frequently pivoted on the upper end of the upper secondary yoke and on the lower end of the lower secondary yoke. In particularly long setups, tertiary yokes may also be provided on the lower and upper ends of the upper and lower secondary yokes, respectively. It should be noted that the terms "upper" and of "lower" are here used relatively only and refer to being distal or proximal, respectively, from the axis at which the wiper arm is pivoted on the vehicle. The ends of the tertiary yokes, and any secondary yoke end to which a tertiary yoke is not pivoted, are formed as claws that engage around a backing strip that in turn carries an elastomeric wiper blade. The main yoke may carry two such pairs of secondary yokes carrying respective tertiary yokes for carrying two such backing strips and blades.
A problem at high vehicle speed is that the air moving over the windshield can in effect get under the wiper blade assembly and lift it from the windshield, reducing the wiping effect. Accordingly it is known, for example from German patent document 3,004,478 to incorporate one or more air deflector members in the central main yoke of the blade assembly so that as the velocity of the moving air stream increases, the force with which the assembly is pressed down on the windscreen is also increased. However, this known method does not take account of the likely variation in pressures generated on the wiper blade by the secondary and/or tertiary yokes and although some overall improvement can be expected by the use of air deflector members on the main yoke, such use has not, thus far, solved the problem of securing good end-to-end wiping performance on a range of different windshield profiles over a range of different moving air stream configurations.